1. Field of the Invention
The present invention relates to a thin film magnetic recording/reproducing head used for a magnetic disk apparatus, and a magnetic disk apparatus or recording/reproducing apparatus including the same.
2. Description of the Related Art
In a magnetic disk apparatus, data are written or read on or from a recording medium or magnetic disk by a magnetic head. To increase a recording capacity per unit area of a magnetic disk, an areal recording density is required to be enhanced. The areal recording density can be enhanced by increasing a track density and a linear recording density. To increase the track density of the above two factors for enhancing the areal recording density, the track width of the magnetic head is required to be made fine and precise. As the track width becomes narrower, a reproducing output becomes smaller, and therefore, to attain a narrower track width, a reproducing head is required to be changed from a MR (Magneto-resistive) head having been extensively available at present to a GMR (Giant Magneto-resistive) head.
To form a magnetic core, including a track portion, of a recording head, a process using dry etching such as ion milling or a process using frame plating has been widely used.
A process of forming an upper magnetic core by using dry etching such as ion milling is performed by forming a magnetic film made from permalloy or the like by sputtering; forming a resist pattern on the magnetic film by photo-lithography; and selectively removing the magnetic film by dry etching such as ion milling by use of the resist pattern as a mask.
On the other hand, the process of forming an upper magnetic core by frame plating is performed by forming an undercoat for plating on a substrate; forming a resist frame on the substrate by photo-lithography; plating the substrate, on which the frame has been formed, with a magnetic material such as permalloy to form a magnetic film; masking a region surrounded with the frame with a resist by photo-lithography; and removing an unnecessary portion of the magnetic film by wet etching.
To increase the recording density of a magnetic disk apparatus, as described above, the track width of a magnetic head is required to be made fine and precise. On the other hand, to avoid magnetic saturation at a track portion located at the end of an upper magnetic core of a magnetic head, the thickness of the upper magnetic core is required to be made as large as being in a range of 2 μm to several μm. The upper magnetic core having such a large thickness, however, cannot be accurately formed by the process using dry etching such as ion milling. This is because a variation in dimension of a resist pattern formed by photo-lithography is added to a variation in dimension of a magnetic film caused upon dry etching of the magnetic film using the resist pattern as a mask. On the contrary, the above magnetic core having the large thickness can be accurately formed by the process using frame plating. This is because a variation in dimension of a resist frame becomes a variation in dimension of the magnetic film for forming the upper magnetic core as it is. Accordingly the process using frame plating is superior in dimensional accuracy to the process using dry etching such as ion milling.
Since the thickness of a resist used as a resist frame must be larger than a plating thickness, it is required to be significantly larger than a film thickness used for fabrication of a semiconductor device, that is, about 1 μm, more concretely, in a range of at least 2-3 μm to 10 μm. In a mirror projection aligner or a stepper as an exposure system, the resolution (R) of the resist pattern is expressed byR=k1·λ/NAwhere k1 is a constant, NA is the numerical aperture of a lens, and λ is a wavelength of exposure light. Also the depth of focus (DOF) of the above exposure system is expressed byDOF=k2·λ/NA2where k2 is a constant.
As is apparent from these equations, to increase the resolution, the wavelength of exposure light may be shortened and the numerical aperture of the lens be increased; however, in this case, the depth of focus becomes shallower. Consequently, to make fine the resist pattern, it is required to make thin the thickness of the resist as well as shorten the wavelength of exposure light and increase the numerical aperture of the lens. Alternatively, to obtain a necessary depth of focus with the resolution fixed, it is required to shorten the wavelength of exposure light and reduce the numerical aperture of the lens. In the case of using a widely available high pressure mercury lamp as a light source, if exposure is performed using g-line (wavelength: 436 nm), resolution up to 2.0 μm can be attained for the resist having a thickness of 8 μm; and if exposure is performed using i-line (wavelength: 365 nm), resolution up to 1.3 μm can be attained for the resist having the thickness of 8 μm. In the case of using i-line for exposure, resolution up to 0.5 μm can be attained by thinning the resist to 1 μm or less. The resist having a thickness of 1 μm or less, however, is too thin to be used for a resist frame, and therefore, such a resist cannot be used for formation of a magnetic core.
Japanese Patent Laid-open No. Hei 7-296328 discloses a method of defining a track width of a recording head by forming a resist layer having a thickness ranging from 0.7 to 0.8 μm on a SiO2 (silicon dioxide) film, forming a notch structure by selectively etching the SiO2 film using the resist layer as a mask, and forming a magnetic film in the notch structure. The method disclosed in this document, however, is poor in dimensional accuracy because etching is performed using the resist pattern as a mask. That is to say, a variation in dimension of the resist pattern is added to a variation in dimension of the notch structure formed by etching. Another problem of this method is that a magnetic pole end of an upper magnetic pole layer is emerged at the face, opposed to a medium, of a magnetic core, and accordingly a magnetic flux leaked from the magnetic pole end of the upper magnetic pole layer may write or erase signals, to thereby enlarge an effective track width.
To solve the above problem, it may be considered to form the upper magnetic pole layer by frame plating in such a manner as to prevent the magnetic pole end of the upper magnetic pole layer from being emerged at the face, opposed to a medium, of the magnetic core; however, in this case, there arises a problem that it is difficult to accurately form a frame for plating because of halation from a coil insulating film as shown in FIG. 1. FIG. 1 shows that a positive-type photo-resist layer 3 is exposed by reflected light from a insulating film 2 on a predetermined substrate 10. In FIG. 1, numeral 1 designates a conductive coil. This reflection light causes the above-said halation of the positive-type resist layer.
To cope with such an inconvenience, Japanese Patent Laid-open No. Hei 6-20227 discloses a method of forming a frame for a rear portion of a magnetic core using a negative resist.
In the invention disclosed in Japanese Patent Laid-open No. Hei 6-20227, however, since a end portion of the magnetic core is formed after formation of a stepped portion of the coil insulating film, the thickness of the resist becomes large at the stepped portion of the coil insulating film, and thereby it is difficult to form the resist pattern of about 1.5 μm. Also when the track width is made as narrow as about 1.5 μm, magnetic saturation occurs at the narrow portion, to cause a problem that it is difficult for a magnetic field to be emerged to the face, opposed to a medium, of the magnetic core. Further, to enhance the data transfer speed of a magnetic disk apparatus, it is required to improve characteristics of a recording head at a high frequency, and to meet such a requirement, it is necessary to most suitably select a material used for the upper magnetic core, more concretely, such that the magnetic domain is directed in the track width direction and the resistivity is increased to reduce an eddy current loss. On the other hand, to avoid occurrence of magnetic saturation at the end portion of the magnetic core as described above, it is required to use a material having a high magnetic saturation density. Eventually, it is difficult to select a material capable of satisfying these requirements.
For this reason, conventionally, there have been not manufactured yet a recording/reproduction separation type thin film magnetic head having a narrow track width of 1.5 μm or less or capable of keeping up with data transfer at a high speed, and a magnetic disk apparatus including such a thin film magnetic head and exhibiting an areal recording density of 5 Gbit/in2 or more.